The present invention relates in general to the field of gas metal arc welding and electrodes for gas metal arc welding. More specifically, the present invention relates a straight polarity (DCEN) welding configuration and a metal-cored wire electrode having a composition functioning as an arc stabilizer.
Gas metal arc welding (GMAW) is a welding process in which an electrical arc between a filler metal and a work piece heats the filler metal and the work and welds them together. The filler metal is usually a consumable electrode which is fed into the process as fast as it is consumed. The electrical arc is formed between the tip of the consumable electrode and the metal of the work piece. The GMAW welding process can be used to join two pieces of sheet metal together, as well as in many other applications. An example of a welding gun and an arrangement for GMAW is schematically shown in FIG. 1. A consumable welding electrode 14 is fed into the welding process through a welding gun 10. Electrode 14 is melted by an electrical arc 18 established between the electrode and the work piece consisting of metal sheets 11 and 13. Externally supplied gas, such as Ar, CO2 or mixtures thereof, enters the welding process through a gas nozzle 12 in welding gun 10 and shields the arc, the tip of the electrode and the pool of molten metal 15 by forming a gas shield 16. The advantages of the GMAW process is the high quality weld that can be produced faster and with very little spatter and loss of alloying elements due to the gas shield and a stable electrical arc.
The consumable electrode in FIG. 1, which is melted by the electrical arc, is transported by the arc to the work piece to serve as a filler metal. The arc produces the heat for the welding process and is maintained by the electron flow from a cathode (positive terminal) and an anode (negative terminal). In the GMAW context both the consumable electrode and the work piece can function as a cathode or an anode. In a straight polarity configuration the electrode is negative and the work piece is positive, which configuration is called direct current electrode negative (DCEN). In a reverse polarity configuration the electrode is positive and the work piece is negative, which configuration is called direct current electrode positive (DCEP). In a schematic illustration of a DCEP configuration in FIG. 2(a) the electron flow is directed from a negatively charged work piece to a positively charged electrode, while the flow of positively charged ionized particles of the shielding gas flows to the negatively charged work piece, bombarding it and adding to the overall heating of the work piece and causing deep penetration of the weld into the work piece. In a schematic illustration of a DCEN configuration shown in FIG. 2(b) the electron flow is directed from a negatively charged electrode to a positively charged work piece, while the flow of the ionized shielding gas flows from the work piece to the electrode. Therefore, in the DCEN configuration the heat flow is directed away from the work piece toward the electrode, resulting in a higher electrode melting rate and a lesser heating of the work piece.
The GMAW process normally uses a direct current electrode positive (DCEP) configuration, which produces a stable arc and low spatter in GMAW applications the direct current electrode negative (DCEN) configuration results in a non-stable erratic arc, sputter, produces poor quality weld, and, therefore it is rarely used.
Nevertheless, it is quite attractive to try to use the DCEN configuration for various welding applications where the lower amount of heat supplied to the Work piece and shallower penetration would be advantageous. One of the examples of such advantageous applications is gas metal arc welding of thin sheets of metal. The excessive heat flow from the electrode to the metal in the DCEP configuration bums through a thin sheet metal and severely damages the work piece. The DCEN welding process also allows to perform the welding with lower or more controlled penetration into the base material, as well as limit the dilution and warpage of the material while maintaining high deposition rates. If the problem of stabilizing the arc during the DCEN welding process could be successfully solved, then the high quality weld and high deposition rates could be obtained in a controlled straight polarity welding applications.
One of the ways to stabilize the arc of the GMAW process is to alter the composition of the wire electrode to add fluxing and alloying elements which function as arc stabilizers. Conventional solid electrode wires are not stable in DCEN welding process and produce a large amount of spatter that must be removed after the welding. In addition, the arc in the solid wire welding process is erratic and hard to control, Carbon steel metal cored wires for GMAW are flux-cored wires used as electrodes comprising a flux filler core encapsulated by a metal sheath. The core of the wire electrode is made of fluxing and alloying compounds, which core becomes a deposited weld material. The composition of the core determines the composition and physical characteristics of the weld metal. Generally, the compounds contained in the core are selected to function as deoxidizers, alloying elements, arc stabilizers and may provide additional shielding gas. Metal cored wires provide the ability to add various materials to the core, influencing the welding characteristics and conditions in a way that overcomes traditional flaws of the DCEN process, Therefore, it would be desirable to have an electrode wire with a core composition allowing to maintain the stability of the arc in a straight polarity welding process while exhibiting the desired high deposition and fast fill characteristics.